Firstly, hello. I have used this site in the past but I couldn't remember my old user name so I started from scratch.

Ive got to put in a base for a log cabin of two rooms which are 6mL x 4mW x 3mH and 3.5mL x 3.5mW x 2.5H.

As it will be used for accomodation I was going to build a floor of 100mm hardcore, 50 - 75 mm polystyrene, a heavy guage polythene sheet and 75mm concrete but please advise if this is OTT. What width and depth of foundation should I use for a building of the above dimensions?

Also, all concrete will be mixed on site. I can't see a way out of it as the nearest road is 400 metres away and a mixer lorry wont get any nearer to the site. If it were pumped from the road, the road would be blocked by the lorry for the duration of the pour. In order to estimate what im going to need what volume is one tonne of mixed aggregate when mixed? I realise its roughly a cubic metre dry but it appears to "shrink" when it goes in the mixer.

in absence of other more knowledgable replies, ill take a guess that it'll need to be a class 1 base.... non standard construction, habitable etc...which would mean 1m deep footings (ish, could be deeper and reinforced dependent on ground/trees etc), 600x250mm of concrete in the bottom, brick/block up to splash, 150mm hardcore, 80mm cellotex, 100mm concrete, 75mm reinforced screed including dpm and thermal break round the edge...just ring building control for a spec, theyre the people who have to pass it...

cellotex has twice the insulation value of polystyrene so 75mm of jabfloor is nowhere near enough...

_________________All my advice should be taken with a rather large pinch of salt, all the gear, absolutely no idea whatsoever ;)

I was involved in building a similar if bigger cabin, 9.5x4.5m, two beds hall and shower room, all passed by building regs, no planning consent required, within permitted development rights. It was timber framed 90mm kingspan in the walls, oak clad to the outside.

The base was 150mm concrete, with 200mm thickened round the perimeter, reinforced with 2 sheets of mesh, 50mm in from top and bottom. Additional mesh in thickened area.

Ground plate of timber frame was set on a single course of engineering bricks, 90mm celotex laid on 1000 gauge DPM in between this course. Chipboard floating floor laid over this.

The ground was clay, raft was designed to cope with this, cleint was a structural engineer, so I'm guessing it is correct! All signed off by BCO as habitable space.

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